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9.1. Creating Basic Filters

Creating a filter involves five basic steps:

1.

Create a class that implements the Filter interface. Your class will need three methods: doFilter, init, and destroy. The doFilter method contains the main filtering code (see Step 2), the init method performs setup operations, and the destroy method does cleanup.

2.

Put the filtering behavior in the doFilter method. The first argument to the doFilter method is a ServletRequest object. This object gives your filter full access to the incoming information, including form data, cookies, and HTTP request headers. The second argument is a ServletResponse; it is mostly ignored in simple filters. The final argument is a FilterChain; it is used to invoke the servlet or JSP ...